1. Field of the Invention
This invention relates to a video tape recorder system, and more particularly to a video tape recorder system which employs a video tape having the width of 4 mm as media for recording video and audio signals.
2. General Description of the Prior Art
Recently, an increasing demand for reducing the physical size of a video tape recorder(VTR) has existed. In conjunction with the achievement of this demand, it will become very critical to employ a narrower video tape as the recording media for use in the VTR, due to which the VTR system can be designed and made to a considerably small phyical size. Considering this, there has been developed a VTR system which employs a video tape having the width of 8 mm. However, the VTR system using the 8-mm tape is not yet small in size enough to provide its user with a full satisfaction for the portable use. Accordingly, a further demand for a more size-reducible VTR system which employs a narrower tape than the 8-mm tape has remained unsolved.
As a prior art, FIG. 1a and 1b respectively show a tape format and a frequency distribution diagram in a 1/2-inch video tape for use in a conventional VTR system. This VTR system of the prior art adopts as its scanning method a helical scanning in which the head drum has two video heads at an interval of 180.degree. in degrees and one field of video signals is recorded into one line of video track pitch at a slant angle to the traveling direction of the tape. As its recording method it uses a azimuth method in which the head gap between its writing(recording) head and its reading(reproducing) head is operated with a tilt of a certain angle.
Referring to FIG. 1a showing the tape format of the prior art which uses the 1/2-inch(12.65 mm) video tape, an audio tape width C for writing the audio signals is located in a 1-mm wide strip from the utmost top of the tape, an audio-to-video guide width F for precisely dividing the audio signals and video signals is set into a 0.15-mm wide strip below the audio track width C, and an upper overlap area H1 is located below the audio-to-video guide width F with a 0.265-mm width. In a 0.75-mm wide strip from the bottom of the tape is located a control track width D for writing control signals to control the transport of the tape. A control video guide width G for dividing the control signals and the video signals into two areas is set into a 0.15-mm wide strip to the upper part of the control track width D and a lower overlap area H2 is located to the upper part of the control video guide width G with a 0.265-mm width. A video full width B including the upper and lower overlap-areas H1 /and H2 has a 10.60-mm wide area of tape. This format enables to record video signals of enough frquency bands on the tape. Referring to FIG. 1 b showing the frequency bands distribution in the video full width B of the 1/2-inch video tape, provided that the maximum frequency range roughly reaches to 7 MHz, the component COL of color signals becomes 629 KHz, and the carrier frequency-modulated(FM) signals from the luminance signals amounts to 3.4 MHz-4.4 MHz. Thus its frequency deviation has come to use 1 MHz.
As stated above, the 1/2-inch tape format of VHS type has not any difficulty in recording the audio signal, the video signal and the control signal together on the tape, but because of its very large width being 12.65 mm wide, the diameter of the drum for the VTR system becomes large, for example, to be 62 mm wide, which consequently results in a large size of the hardware mechanism for operating the system. Furthermore, because the control signal to control the transport speed of the tape is independently recorded into the control track width, a control head to read the control signal must be independently installed, which also has caused a problem in size reducing and cost saving. As a result, the VTR system having the 12.65 mm wide video tape is not adequate for portable use.
As another prior art, FIG. 2a and 2b respectively show a tape format and a frequency distribution diagram in a 8-mm wide video tape for use in another VTR system, by which the physical size of a VTR system is considerably reduced to be more adequate for portable use. Referring to FIG. 2a, a first option track C' is located in the upper part of the 8-mm tape width A', a first guide width F' is located below the first option track C' for dividing other signal area next to the first guide width F' and a first overlap area H1' is located below the first guide width F'. In the bottom part of the tape width A' is located a second option track D', a second guide width G' is located above the second option track D' to divide the second option track and other area, and a second overlap area H2' is located above the second guide width G'. The area between the first guide width F' and the second guide width G' including both the first and second overlap areas H1' and H2' amounts to the video full width B', which records the video signal, the audio signal and the control signal altogether. Referring FIG. 2b showing the frequency band distribution in the video full width B' of the 8-mm video tape, automatic track finding(ATF) pilot signals which are used to control the traveling of the tape are set into the lower frequency band area f1=102.5 KHz, f2=118.9 KHz, f3=165.2 KHz and f4=148.6 KHz, provided that the maximum frequency range roughly reaches to 7 MHz. Also, its audio component AUD is set into the frequency 1.5 MHz and the carrier frequency of luminance signals is set into 4.2 MHz to 5.4 MHz by which its frequency deviation has come to use 1.2 MHz.
In the 8-mm video tape as mentioned above, the diameter of its drum to read out the video signal, the audio signal and the control signal from the tape is reduced to 40 mm, a considerably small size, compared with that for the 12.65-mm tape. However, this 8-mm VTR system has not yet achieved the completely satisfactory size reduction of the VTR apparatus for the portable purpose due to its comparatively large hardware mechanism. This has raised an increasing demand for the compact-sized VTR system intended for portable use with more diverse functions serviced.